Lag Screw Theory

- Discussion:
- involves placement of one or more screws across a frx or osteotomy site to achieve interfragmentary compression;
- note that the direction along which the compression acts (inclination of lag screw) must coincide well w/ perpendicular axis of the fracture surface;
- as Johner, et al (1983) have shown, frx sliding will occur if the compression is applied at an angle greater than 20 deg in relation to axis
perpendicular to the fracture surface;
- it has been written that if more than one lag screw can be positioned across a frx site, then plate fixation of the frx is not necessary;
- fortunately, only one or two disaters w/ this statedgy are required for the orthopaedist to realize that this is not true;
- self tapping screws:
- if self tapping screws are inadvertently angled, they will cut a new path and destroy already cut thread, which is a disadvantage;
- self tapping screws should therefore not be used as lag screws;